Entomopathogenic Bombs – Sweet Potato Weevils Be Gone

View the project report

Commodities

• Vegetables: sweet potatoes

Practices

• Pest Management: biological control

Sweet potato is economically and culturally important in Hawaii. Sweet potato was the highest revenue-generating vegetable crop in Hawaii until challenged by multiple pests, in particular the sweet potato weevil (Cylas formicarius elegantulus). While weevil feeding may cause vine damage, the more serious problem is to the tubers. Larvae tunnel resulting in spongy tuber that is dark in color. Additionally, larval feeding causes tubers to develop a bitter taste and a terpene odor. Losses to the weevil range from 30 to 97% across farms. Producers in Hawaii have turned to pesticide-intensive management tactics spanning the time from planting to harvest. Growers sometimes rely upon weekly insecticide applications to ensure a marketable crop. Non-chemical based integrated pest management strategies are needed and entomopathogenic nematodes (EPN) are a promising candidate. The weevils are susceptible to Heterorhabditis sp. and Steinernema sp. and have met with some success in other sweet potato growing areas. We propose to use EPN living bombs to control the sweet potato weevil. Living bombs are the application of EPN infected insect cadavers rather than direct aqueous application of the EPN. One objective will be to demonstrate the efficacy of H. indica and S. feltiae in reducing weevil damage in sweet potato in Hawaii. Traditional EPN application methods utilize inundative release of billions of EPN/ha in an aqueous solution. Delivery of the EPN in cadavers will allow for lower numbers and a consequently less expensive tool for growers. Another objective will be to compare the efficacy of different delivery methods of H. indica and S. feltiae. All EPN applications (sprays or bombs) will be compared to the standard practices of cooperating sweet potato producers. Since the focus is to transfer pipeline technologies to growers, our final objective is to convey the information to growers and other practitioners. We will develop videos, extension publications, newsletter articles, and scientific publications to share information. Initially, we will serve as a source for the EPN via a fee-for-service while the nascent demand for EPN builds and before commercial operations enter the Hawaii market. The potential impact of the project is the adoption of environmentally safe and sound biological control for sweet potato weevil by the key sweet potato producers that will then model and influence adoption by fellow sweet potato growers. The co-PIs have statewide connections to share project outcomes through social media, e-mail lists, and newsletters. The project team will work closely with leading growers and extension agents to foster adoption. Our longterm goal is to promote sustainable sweet potato cultivation through economic and environmentally sound pest management.

We propose to use entomopathogenic nematodes (EPN) living bombs to control the sweet potato weevil. We have two research objectives and three education objectives. Our research objective 1 will be to demonstrate the efficacy of Heterodera indica and Stienernema feltiae, different species of EPN, in reducing weevil damage in sweet potato. Research objective 2 will be to compare the efficacy of spray applications to living bomb delivery of H. indica and S. feltiae documenting that fewer EPN are needed for effective weevil management when delivered as living bombs. Our educational objectives are (1) to impart knowledge about EPN for IPM control of sweet potato weevil, (2) to illustrate the application of EPN living bombs, and (3) to demonstrate the utility of EPN living bombs as an additional IPM tool for control of sweet potato weevils.